Range finder

ABSTRACT

A system and method for measuring a height of objects on a moving surface comprising providing a linear image sensor positioned transverse to a direction of travel of the moving surface, and at least one light source positioned collinear to the linear image sensor and proximate to an edge of the moving surface so that the light source projects a unique patterned light sequence across a width of the moving surface, detecting a transverse shift in a portion of the unique patterned light sequence with respect to the direction of travel of the moving surface as an object passes through the unique patterned light sequence, determining an amount of shift of the portion of the unique patterned light sequence, and determining a height of the object based on the portion of the unique patterned light sequence shift.

CLAIM OF PRIORITY

This application claims priority to U.S. Provisional Patent ApplicationNo. 60/868,245, filed Dec. 1, 2006, the entire disclosure of which isincorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to conveyor systems and, moreparticularly, to conveyor systems having networked components.

BACKGROUND OF THE INVENTION

Referring to art FIG. 1, a known dimensioning system 10 includes aconveyor system 12 that moves items along a path of travel, and acomponent system 14 adjacent to the conveyor system that tracks packagesbeing moved by the conveyor system. Conveyor system 12 includes a numberof rollers 16, a belt 24, a bed 18 and a tachometer 20. It should beunderstood that the conveyor can move the items through the path oftravel by means other than belts, for example by driven rollers. Rollers16 are motor-driven rollers that move conveyor belt 24 in a directiondenoted by arrows 26 over bed 18, which provides support to the belt.For purposes of the present discussion, the direction corresponding tothe start of conveyor system 12 is referred to as “upstream,” whereasthe direction in which conveyor belt 24 moves is referred to as“downstream.”

Tachometer 20 is beneath and in contact with the surface of conveyorbelt 24 and rotates with the belt as the belt moves in the direction ofarrows 26. As tachometer 20 rotates, it outputs a signal comprising of aseries of pulses corresponding to the conveyor belt's linear movementand speed. Tachometer 20, and other devices that provide signalscorresponding to the rate of movement of a conveyor belt, from which thelocations of items moving in a path of travel along the belt can bedetermined, should be understood by those of ordinary skill in the art.In general, the number of pulses output by tachometer 20 corresponds tothe linear distance traveled by the belt, while pulse frequencycorresponds to the belt's speed. The number of tachometer pulses perunit of measurement defines the resolution of the tachometer and itsability to precisely measure the distance that the conveyor belt hasmoved. Tachometer 20 may be replaced by a shaft encoder, particularlywhere less accurate measurements are needed.

Component system 14 includes a dimensioner 28, a plurality of barcodescanners 32, and a computer 36, all of which are attached to a frame 38.Frame 38 supports dimensioner 28 and at least one barcode scanner 32horizontally above conveyor belt 24 so that beams of light emitted bythe dimensioner and scanners intersect the top surfaces of packagesmoved by the belt. Frame 38 also supports additional scanners 32vertically adjacent to conveyor belt 24 so that beams of light emittedby these scanners intersect the side, back, front or bottom surfaces ofpackages moved by the belt. One example of prior art scanners includeQUAD X laser barcode scanners manufactured by Accu-Sort Systems, Inc. ofTelford, Pa., although it should be understood that cameras or othersuitable barcode readers could be used, depending on the needs of agiven system.

As should be understood in this art, dimensioner 28 detects one or moredimensions of an item on a conveyor. The dimensioner is disposed alongthe conveyor at a known position relative to the bar code readers. Whena package moving along the conveyor reaches the dimensioner, thedimensioner processor opens a package record, determines height, widthand length, associates that data in the package record, and outputs thedimension data to the system processor in association with tachometerdata that corresponds to the package's location at the dimensioner. Uponreceiving the dimensioner data, the system processor opens a packagerecord and associates with the package record the dimension andtachometer data received from the dimensioner.

The system processor also sets an open read window variable and a closeread window variable for the barcode scanner. The open read windowvariable for the barcode scanner is equal to the tachometer value forthe downstream-most point on the package, plus a known distance (intachometer pulses) between the dimensioner and a predetermined positionin the path of travel with respect to the barcode scanner. The closeread window variable for the barcode scanner is equal to the tachometervalue for the upstream-most point on the package, plus a known distance(in tachometer pulses) between the dimensioner and the predeterminedposition with respect to the barcode scanner.

As should be understood in this art, barcode reader 32 may comprise alaser scanner that projects a plurality of laser lines on the belt, forexample in a series of “X” patterns. The scanner outputs a signal thatincludes barcode information reflected back from the laser lines and abarcode count, which indicates the position in the X patterns at whichgiven barcode information was seen. Thus, the barcode count provides thelateral position on the belt, and the longitudinal position with respectto the centerline of the X patterns, corresponding to the barcodeinformation. The barcode scanner assembly has a photodetector disposedalong the conveyor immediately upstream from the X patterns. A processorat barcode scanner assembly 32 monitors the photodetector's outputsignal and thereby determines when the package's front and back edgespass the photodetector. The barcode scanner also receives the tachometeroutput. By associating the passage of the package's front and back edgesby the photodetector with the tachometer data, the barcode scannerprocessor determines when the package passes through the X patterns. Thebarcode scanner processor accordingly determines when valid barcode datamay be acquired for the package and acquires the barcode data duringthat period.

The barcode processor accumulates barcode data while a given packagepasses through the X patterns and transmits the accumulated barcode datato the system processor when the package reaches a predetermined pointin the path of travel following the barcode scanner. More specifically,the barcode scanner processor knows when the front edge of the packagepasses by the barcode scanner photodetector. After acquiring thepackage's barcode data over a period based on the package's length, thebarcode scanner processor holds the barcode data until a tachometervalue the barcode scanner processor associates with the barcode dataaccumulates to a point indicating that the front edge of the package isat the predetermined point downstream of the scanner. The predeterminedpoint is defined so that the longest package the system is expected tohandle can clear the scanner's X patterns. The barcode scanner processorthen outputs the barcode data to the system processor.

The system processor relies on tachometer pulses to correctly associatebarcode data with a package record. The system processor determines theaccumulated tachometer value at the time the barcode data is receivedfrom the barcode scanner processor. The open read window and close readwindow barcode variables for each package structure correspond to thedistance between the dimensioner and the predetermined point downstreamfrom the barcode scanner. Thus, the system processor compares thetachometer value associated with the received barcode data with the openread window and close read window barcode variables for the open packagestructures it maintains in memory. If the tachometer value is betweenthe open read window barcode variable and close read window barcodevariable for any open package structure, the system processor assignsthe barcode data to that package record. If the tachometer value doesnot fall within the open window and close window barcode variablesstored for any open package record, the barcode data is not assigned toa package record.

The described system of FIG. 1 was directed to barcode scanners thatproject an X-pattern across the belt. It should be understood to thoseskilled in the art that X-pattern scanners can be replaced with linescan cameras for detecting and reading barcodes. Line scan cameras likebarcode scanners are bulky and heavy and require more than onetechnician to install and calibrate the scanner in scanning tunnel.

To initially set up and calibrate system 10, the camera tunnel frame isset up and the barcode cameras are mounted to the frame so that they arepositioned and orientated properly with respect to the conveyor belt.This requires several technicians to lift the cameras into place in thetunnel and secure them to the frame. In general, prior art cameras areunitary structures that are bulky and cumbersome for a single technicianto lift and secure. Moreover, because the cameras operate with highpower, a large amount of heat must be expelled from the camera housingso as not to damage the camera electronics and optics. Thus, fans areenclosed in the camera housing to pull air through the housing to cooloff the internal components.

Technicians connect each camera to a computer to individually calibrateand set the camera's operating parameters. The technician inputs camerainformation directly into the camera processor via the computer and maysave certain camera settings to a dongle or other portable storagedevice. Calibration data may include the angle of orientation of thecamera, the height of the camera and the location of the camera withrespect to the belt and the dimensioner. Once each camera is calibratedand set-up in the tunnel, the cameras are connected to a centralcomputer that receives information captured and processed by eachcamera. However, should a camera break or need to be serviced, a fullcalibration and set-up is necessary for the camera being replaced andpossibly for the overall tunnel to ensure that all components of thetunnel are properly aligned.

In the system shown in FIG. 1, dimensioner 28 is a triangulation typedimensioner similar to those disclosed in U.S. Pat. Nos. 6,775,012,6,177,999, 5,969,823, and 5,661,561, the entire disclosures of which areincorporated by reference herein. With regard to these embodiments,dimensioner 28 comprises a light source, such as a laser and a rotatingreflector disposed within the dimensioner housing that produce ascanning beam (denoted in phantom at 40) that is directed down atconveyor belt 24. That is, the rotating reflector scans the single pointlight source across the width of belt 24. Each angular position of thereflector represents an x-axis location across the belt. Scanning beam40 intersects belt 24 at line 42 in a manner that is transverse (x-axis80) to the belt's linear movement (y-axis 82) in the path of travel at afixed angle with respect to an axis normal (z-axis 84) to the belt'ssurface. Packages moving on belt 24, such as package 62, intersectscanning beam 40, thereby creating an offset in the scanning beam in they-direction (along y-axis 82). In particular, the laser light source ispositioned downstream in the y-axis 82 direction so that the plane oflight is reflected at an angle from z-axis 84. Thus, as a box movesdownstream the intersection of the plane of light is a continuous lineacross the belt in along x-axis 80. When a box intersects the plane oflight, the portion of the plane intersected by the box will shiftforward toward the light source since the light on the box travels ashorter distance than the light that intersects the belt on the left andright sides of the box. This offset or shift in the light on the boxsurface is proportional to the height of the box.

Both conveyor belt 24 and the packages thereon reflect light created bythe scanning beam back to the rotating mirror, which reflects light to alinear array of line scan CCD detectors or a CMOS imager (not shown)within dimensioner 28. The array is oriented parallel to y-axis 82.Because the rotating mirror reflects both the outgoing and reflectedlaser light, the mirror returns the reflected light to a constant x-axisposition, but the reflected light shifts in the y-directioncorrespondingly to the shift in line 42 caused by the height of apackage 62 and the angle at which the scanned laser beam intersects thebelt. Thus, the linear array of CCD or CMOS detectors must be accuratelyaligned in the y-direction to thereby detect the return light's y-axisshift. Moreover, because the array is made up of a single line of pixelsensors, the alignment is critical to detect the reflected light. If theaxis of the linear sensor is misaligned with the fixed x-axis pointwhere the mirror directs the reflected light, the sensor will not detectthe change in height. The rotating mirror's angular position correspondsto the x-axis position of any given point of reflected light.

Dimensioner 28 generates a signal representative of the height of anobject such as package 62 across conveyor belt 24 as described by they-axis offset detected in scanning beam 40. The signal is alsorepresentative of the x-axis positions of the height data by associationof that data with the mirror's angular position. Based on the heightdata and corresponding x-axis data, the dimensioner processor (notshown) determines the cross sectional height profile an object on thebelt and, by accumulating such profiles along the object's length, theobject's three dimensional profile.

As with the camera, technicians must lift and hold the dimensioner inplace while it is secured to the tunnel frame. Next, levels are used toensure that the dimensioner's detector is parallel to the face of theconveyor belt. If the dimensioner's detector array is out of asubstantially parallel adjustment with respect to the belt, thedimensioner may obtain inaccurate dimensions of the object.Additionally, as previously described, should the line scan array notalign properly with the rotating mirror, e.g. because of slightmisalignments between the array and the rotating mirror, the dimensionermay not detect any shift in the light. Moreover, the rotating mirror maybecome misaligned during shipping or installation through jarring of thedimensioner.

SUMMARY

The present invention recognizes and addresses the foregoingconsiderations, and others, of prior art constructions and methods.

These and/or other objects are achieved in a preferred embodiment of amethod for measuring a height of objects on a moving surface comprisingproviding a linear image sensor positioned transverse to a direction oftravel of the moving surface, and at least one light source positionedcollinear to the linear image sensor and proximate to an edge of themoving surface so that the light source projects a unique patternedlight sequence across a width of the moving surface, detecting atransverse shift in a portion of the unique patterned light sequencewith respect to the direction of travel of the moving surface as anobject passes through the unique patterned light sequence, determiningan amount of shift of the portion of the unique patterned lightsequence, and determining a height of the object based on the portion ofthe unique patterned light sequence shift.

In some embodiments, the unique patterned light sequence comprises aseries of light bars separated by non-lighted spaces. In otherembodiments, the light bars and non-lighted spaces have at least twodiffering widths. In yet other embodiments, the light bars have at leasttwo differing widths and the non-lighted spaces having at least twodiffering widths that also differ from the at least two differing lightbar widths. The series of light bars and the non-lighted spaces maydefine a plurality of words across the width of the moving surface,where the width of the light bars are selected from approximately oneand three pixels and a width of the non-lighted spaces are selected fromapproximately two and four pixels. The light bars and non-lighted spacesmay have a length in the direction of travel of the moveable surface ofat least 3 pixels.

In some embodiments, the step of detecting a transverse shift furthercomprises detecting edges of the light bars, determining a sequence ofthe light bars and the non-lighted spaces, and extracting at least oneof the plurality of words based on the sequence of the light bars andthe non-lighted spaces. In other embodiments, the step of determining aheight further comprises comparing the amount of shift of the at leastone of the plurality of words to a location of at least one of theplurality of words when the object is not present. In yet otherembodiments, the unique patterned light sequence is formed by adiffractive optical lens.

In some embodiments, a second light source may be provided and the firstand the second light sources are alternately cycled on and off. In otherembodiments, the step of detecting the lighted bar edges furthercomprises the steps of detecting transitions from lighted bars toadjacent non-lighted spaces, and using linear interpolation to determinethe approximate pixel location of each of the transitions.

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate one or more embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof directed to one of ordinary skill in the art, is setforth in the specification, which makes reference to the appendeddrawings, in which:

FIG. 1 is a prior art schematic representation of a dynamic dimensioningsystem;

FIG. 2 is a block diagram of a dynamic dimensioning system in accordancewith an embodiment of the present invention;

FIG. 3 is a schematic representation of a portion of the dynamicdimensioning system of FIG. 2;

FIG. 4 is a block diagram of a camera for use in the dynamicdimensioning system of FIG. 2;

FIG. 5 is a perspective view of the camera shown in FIG. 4;

FIG. 6 is an exploded perspective view of the camera shown in FIG. 4;

FIG. 7 is an partial exploded perspective view of the camera shown inFIG. 4;

FIG. 8 is an exploded perspective view of an illumination module for usein the camera shown in FIG. 5;

FIG. 9 is a perspective cutaway view of the illumination module shown inFIG. 8;

FIG. 10 is a perspective partial cutaway view of the illumination moduleshown in FIG. 9;

FIG. 11 is an exploded perspective view of a camera module for use inthe camera shown in FIG. 4;

FIG. 12 is a perspective cutaway view of the camera module shown in FIG.12;

FIG. 13 is an exploded perspective view of a communication module foruse in the camera shown in FIG. 5;

FIG. 14 is a block diagram of the communication module shown in FIG. 13;

FIG. 15 is a perspective cutaway view of the camera of FIG. 5;

FIGS. 16 and 17 are perspective views of a range finder in accordancewith an embodiment of the present invention;

FIG. 18 is an exploded perspective view of the range finder of FIG. 16;

FIG. 19 is a schematic view of the range finder of FIG. 16;

FIG. 20 is a laser pattern for the range finder in accordance with anembodiment of the present invention;

FIG. 21 is an exploded view of a portion of the laser pattern shown inFIG. 20;

FIG. 22 is a block diagram of the assembly of the camera of FIG. 5;

FIG. 23 is a block diagram of the assembly of the range finder of FIG.16;

FIG. 24 is a plan view of the conveyor and range finder of FIG. 16;

FIG. 25 is a plan view of the conveyor and range finder of FIG. 16;

FIG. 26 is a intensity plot by pixel for the range finder of FIG. 25;and

FIG. 27 is a close up view of the intensity plot of FIG. 26.

Repeat use of reference characters in the present specification anddrawings is intended to represent same or analogous features or elementsof the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference will now be made in detail to presently preferred embodimentsof the invention, one or more examples of which are illustrated in theaccompanying drawings. Each example is provided by way of explanation ofthe invention, not limitation of the invention. In fact, it will beapparent to those skilled in the art that modifications and variationscan be made in the present invention without departing from the scope orspirit thereof. For instance, features illustrated or described as partof one embodiment may be used on another embodiment to yield a stillfurther embodiment. Thus, it is intended that the present inventioncovers such modifications and variations as come within the scope of theappended claims and their equivalents. Additional aspects and advantagesof the invention will be set forth in part in the description whichfollows and, in part, will be obvious from the description, or may belearned by practice of the invention.

Referring to FIG. 2, a dynamic dimensioning system 100 generallycomprises a range finder 102 or other dimensioning device (i.e., adimensioner, light curtains, etc.) for determining the height and roughdimensions of a box being transported on a conveyor, multiple cameras106, 108, 110 and a tachometer 112 connected to at least one camera 106that outputs a signal representative of the movement of the conveyorbelt. The range finder and the cameras are networked together by, forexample, an Ethernet connection 114. While only three cameras are shownin FIG. 2, it should be understood that any number of cameras can benetworked together to form a scanning tunnel. One of skill in the artshould understand that Ethernet is a local-area network (LAN)architecture that uses a bus or star topology and supports data transferrates of 10 Mbps. Ethernet uses the CSMA/CD access method to handlesimultaneous demands and is one of the most widely implemented LANstandards. A newer version of Ethernet, called 100 Base-T (or FastEthernet), supports data transfer rates of 100 Mbps, and the newestversion, Gigabit Ethernet supports data rates of 1 gigabit (1,000megabits) per second.

Referring to FIG. 3, dynamic dimensioning system 100 scans objects, suchas object 103, moving on a conveyor belt 104, decodes barcodes 116located on the object and transmits the information to a host system(not shown) for further processing. Shown in the figure is a top readbarcode camera 106 and range finder 102 in accordance with oneembodiment of the present invention. In general, objects are movedthrough a field of view 118 of range finder 102. Range finder 102detects the presence of object 103 and determines the range, extent andorientation of the object with respect to the conveyor belt. The extentsof object refer to the left and right edges of the object along x-axis80. The range finder generates an object start trigger that notifies thecameras (only one of which is shown in FIG. 3) of the presence of theobject as well as an object end signal. Range finder 102 transmitsheight and extent data to camera module 106, which uses the informationto focus its optics to maximize the efficiency and effectiveness ofdetecting and reading barcode 116.

Referring again to FIGS. 2 and 3, each camera 106, 108 and 110 uses thetachometer data to track the motion of object 103 through a field ofview 120 of the camera's imaging sensor (not shown in FIGS. 2 and 3).Each camera processes the video data stream and locates and decodes anybarcode data present on the object by detecting light reflected from theobject being scanned. Once the object reaches a predetermined distancedownstream from the tunnel system (this point is set by the host), thesystem transmits the barcode data to the host system for furtherprocessing. It should be understood that camera 106 may be mounted todirect its field of view 120 directly onto conveyor 104, or the field ofview may be redirected by a mirror 122 as shown in FIG. 3. Redirect thefield of view allows the camera to be positioned so that its scanningimage is parallel to y-axis 82, where mirror 122 redirects the field ofview along z-axis 84.

For ease of discussion, only one of cameras 106, 108 and 110 will bediscussed in detail, but it should be understood that cameras 106, 108and 110 are structurally and electronically the same. Referring to FIGS.4-6, camera has a chassis module 124, a camera module 126, anillumination module 128 and a distributed processing and communicationsmodule 130. The modular design allows for camera 106 to be disassembledduring installation to reduce the amount of weight that must be liftedand mounted at any given time.

Referring to FIG. 7, chassis module 124 has two fixed brackets 132 and134 for mounting the chassis module to the scanning tunnel. Two hingedbrackets 136 and 138, located on an underside 140 of chassis module 124adjacent to respective brackets 132 and 134, moveably secure distributedprocessing and communications module 130 to the chassis moduleunderside. In particular, distributed processing and communicationsmodule 130 has four fixed pins 135 that are received in slots 137 formedin hinged brackets 136 and 138. Two spring loaded pins 139 are receivedin holes 141 formed in hinged brackets 136 and 138 to releasably securethe communications module to the hinged brackets. Two fasteners 143fasten the ends of moveable brackets 136 and 138 to the chassis moduleunderside 140 to positively maintain the communications module in aclosed position. Fasteners 143 may be screws, bolts, or other suitablefasteners.

Mounted within chassis module 124 are two power supplies 142 and 144that convert AC power into DC power. Power supply 142 providesapproximately 350 watts of DC power for use by distributed processingand communications module 130 and camera module 126. Power supply 144provides approximately 290 watts of DC power for use by illuminationmodule 128. A DC power distribution board (not shown) generates therequired DC voltages that are not provided directly by power supplies142 and 144.

Referring again to FIG. 6, a rear wall 146 is covered by a plurality ofmetal fins 156 for dissipating heat generated by power supplies 142 and144. Mounted on opposite ends 148 and 150 of rear wall 146 are two setsof fans 152 and 154. Fans 152 pull air into chassis module 124, and fans154 push air out. A rectangular opening 155 receives camera module 126,which is secured in place by fasteners, such as screws, bolts or othersuitable fasteners. Chassis module underside 140 defines a plurality ofopenings 158 for receiving heat sinks 240 (FIGS. 5 and 6) fromdistributed processing and communications module 130. Openings 158 aresized and shaped to snuggly fit the heat sinks so that the communicationmodule interior is sealed off from the area surrounding rear wall 146.It should be understood that gaskets (not shown) may be used around theperiphery of the openings to increase the sealing effect, for examplerubber, silicon, or other polymer type gaskets, for example rubber,silicon, or other polymer or elastomer type gaskets.

Referring to FIGS. 8 to 10, illumination module 128 comprises anillumination servo and control system 162, LED boards 164 (only one ofwhich is shown in the Figures), and illumination optics 166. All of thecomponents are mounted in a housing formed from a rear wall 168, a topwall 170, a bottom wall 172 and two end caps 174 and 176. A hole 177 isformed through back wall 168 to allow the camera lens to extend throughinto the illumination module behind illumination optics 166, asdescribed in further detail below.

Illumination servo and control system 162 is mounted on bottom wall 172,connects to LED boards 164 via cables and receives command signals froma processor (not shown in the Figures) in camera module 126, which isused to set the intensity level of illumination for the LEDs. LED boards164 are mounted on back wall 168 by brackets 169, provide a mountingarea for LEDs 180 and conduct away heat produced by LEDs 180 throughmetal fins 182 formed on rear wall 168. In one embodiment, each LEDboard 164 may be six inches long and may contain eighteen LEDs alignedin a single row. The LEDs are arranged in an interleaved pattern so thatif there is a fault in one string of LEDs, the resulting dark LEDs willbe spread out across the boards to thereby maintain a uniformillumination field. In one preferred embodiment, illumination module 128contains six LED boards.

Illumination optics 166 collimates light output of LEDs 180 and focusesthe light into a line that is coplanar with an imaging sensor viewingplane (not shown in FIGS. 8 to 10). Illumination optics 166 comprisestwo separate cylindrical Fresnel lenses generally denoted by 166, whichshows the two lenses as a single unit: the first is parallel to the axisof illumination to focus the LED light to a narrow plane that iscoplanar with the imaging sensor scanning plane, and the second lens isarranged perpendicular to the first to spread out the light from eachLED board along the scan line to cover the full field of view requiredof the system. It should be understood that in other embodiments, asingle Fresnel lens or a refractive optical element can be used in placeof the double Fresnel lens. Fresnel lens 166 is mounted to end caps 174and 176 by mounting brackets 184 and spacers 186. Fresnel lens 166defines an opening 188 to allow light reflected from a surface to reachthe camera optics of camera module 126, as further described herein.

Enclosing the space defined by illumination module back wall 168, topwall 170, bottom wall 172 and end caps 174 and 176 is a shroud 190.Shroud 190 is preferably formed from a transparent material to allowlight from LEDs 180 to pass through the shroud onto the surface beingilluminated and allow reflected light to pass back through to the cameraoptics. Thus, shroud 190 may preferably be formed from any suitabletransparent material, and in one preferred embodiment, the shroud isformed from an optical grade acrylic. A window 192 disposed in anaperture in a front wall 194 of shroud 190 is formed from an high gradeoptical glass, for example float glass or other similar material tominimize distortion of the reflected light returning to the cameraoptics. Window 192 may be secured to shroud 190 by fasteners or othermeans that securely maintains the window in place. Suitable fastenerswould include clips, pins, press-fitting the glass into the shroudopening, etc.

Illumination module 128 is secured to chassis module 124 by a tongue 196(FIG. 6) formed on chassis module 124 that is received in a groove 198formed in bottom wall 172. Once the illumination module groove 198receives chassis tongue 196, a lip 200 formed on top wall 170 is securedto a chassis top wall 202 by fasteners (not shown), for example screws,bolts, etc.

Referring to FIGS. 11 and 12, camera module 126 comprises a body 204, asensor module 206, a fixed focal length lens 208 and a cover 210. Afocus servo module 212 may be a closed loop servo system that controlsthe movement of a motor (not shown) that adjusts the focal lengthbetween main imaging lens 208 and sensor 213. Focus servo module 212receives commands from a camera module processor 214, which are used toadjust the focal length between main imaging lens 208 and sensor 213 bymoving a mirror located between the camera sensor and the fixed optics.Camera module 126 uses a hinged mirror focus system (such as thatdescribed in U.S. Pat. No. 6,801,260 assigned to Accu-Sort Systems,Inc., the entire disclosure being incorporated by reference herein) toadjust the optical distance between the main imaging fixed focus lensand sensor.

Imaging lens 208 may have a fixed focal length of 68.5 mm, 90 mm and 140mm, which should provide sufficient coverage for most applications ofcamera 100 (barcode and OCR applications in auto identificationmarkets). However, it should be understood that other fixed focallengths may be used depending on the application of camera 100. Sensormodule 206 contains two circuit boards (not shown) and an imaging array213. In one preferred embodiment, the imaging array is an 8000 pixellinear array, 4-tap Dalsa charge-coupled device sensor with a videooutput of 8 bits per pixel. It should be understood by those of skill inthe art that other types of CCD sensors may be used. If the sensor boardis operated at its maximum rate of 40-MHz per tap, the sensor board canproduce video at a rate of approximately 160 mega pixels per second.

Referring to FIGS. 13 and 14, distributed processing and communicationsmodule 130 comprises a carrier card 216, a tracking processor 218, avideo processor 220, three COM express modules 222, 224 and 226, and acommunications processor 228. Carrier card 216 provides the platform forall video processing performed by camera module 106. Video from imagingmodule 206 is received by video processor 220 where it is processed inreal time and transferred to COM Express modules 224, 224 and 226 andcommunications processor 228 for further processing. The communicationprocessor and COM Express modules communicate with one another andexternal devices by Ethernet connections 114 through an Ethernet switch230, and/or through a PCI express switch.

Tracking processor 218 receives an input signal from tachometer 112 atinput 232, a trigger signal at input 234 and range information fromrange finder 102 at input 236 and uses the information to track anobject's presence, location and height, as in prior art systems.Tracking processor 218 also provides control and diagnostic commands toillumination module 128 and camera focus servo module 212. Thus, asobjects are transported down conveyor belt 104 (FIG. 2), the trackingprocessor tracks their position relative to camera 106 and height andlocation information on belt 104. In response to this information,tracking processor 218 sends commands to illumination module 128 toincrease or decrease the illumination intensity and to camera focusservo module 212 to adjust the focus of the camera optics to properlyacquire a readable image from the objects. In one preferred embodiment,tracking processor 218 is an i.MX31L manufactured by FreescaleSemiconductor of Austin, Tex.

Video processor 220 provides all high-speed video processing and handlesall real-time control signals from, for example, tachometer 112 andtrigger input 234. Video processor 220 conditions and processestachometer input signal 232 and stamps the tracking information into thelinear sensor image data. Video processor 220 also buffers lines ofvideo data from image sensor 206, packs the lines into 64-bit words andputs the words into the memory of communications processor 228 and COMExpress modules 222, 224 and 226. Video processor 220 maintains aconstant scan speed of imaging sensor 206 based on tachometer inputsignal 232 and the line density configured in the system.

Communications processor 228 receives data input from tracking processor218 and video data from video processor 220. The main function ofcommunications processor 228 is to move image data from video processor220 to COM Express modules 222, 224 and 226. Examples of communicationsprocessor 228 are the MPC8548E, MPC8547E, MPC8545E and MPC8543E allmanufactured by Freescale, Inc. of Austin, Tex.

COM Express modules 222, 224 and 226 allow expansion of camera 106without camera system redesign and can be added at any time to provideadditional functionality without requiring modification to carrier card216. Specifically, modules for performing additional features such asdimensioning, optical character recognition, etc. can be installed incamera 106 at any time through the COM Express modules. The FPGA 220 isconstantly providing camera data to the COM Express modules andcommunication module 228, which can be used for example for OCR ordimensioning. Each COM Express module 222, 224 and 226 has an Ethernetconnection 238 to communications processor 228 through Ethernet switch230, in addition to a PCI express connection.

Each camera has two network ports 178A and 178B that allow the camerasto be linked together. The dedicated network has 100 BaseT Ethernet andhas two hardwired signals: a tachometer pulse and a tachometersynchronization signal. The tachometer signal is sourced by the camerahaving tachometer 112 attached to it. The tachometer synchronizationsignal is a derivative signal of the tachometer signal, which isdirectly transmitted to each of the cameras to ensure that each cameracan accurately track any given package independently of the othercameras. By monitoring these two signals, all of the cameras in thetunnel can stay in perfect synchronization with a package on conveyor104 and with each other by simultaneously counting tachometer pulses foreach package on the conveyor system. Network ports 178A and 178B allowinformation from one camera on the network to be transmitted to anyother camera on the tunnel network. Each camera also contains two ports178C and 178D for connecting to the host system. The first port 178Coutputs an asynchronous signal and the second 178D is a 100BaseTEthernet connection. The imaging network connection outputs image datato the host system for further processing. The PCI Express slot is astandard PCI slot that accepts upgrade cards to provide furtherprocessing features for camera 106. For example, a PCI card may be usedto allow camera 106 to provide real time JPEG compression, which may beoutput to the host system.

The power consumed by camera 106 may be above 180 watts, of which 15 to20 watts may be emitted as light. The remaining power is converted toheat, which must be removed from the camera so as not to damage theelectronics. Because camera 106 contains sensitive optics andelectronics, camera module 126, illumination module 128 andcommunications module 130 are preferably not cooled by traditionalmethods of pulling air through each module, since dirt and debris couldaccumulate on the electronic and optics.

Referring to FIG. 15, the individual modules of camera 106 fit togetherto form a cooling channel 244. In particular, camera module body 204fits into opening 155 (FIG. 6) to form continuous chassis rear wall 146.Illumination module 128 is secured to chassis bottom wall tongue 196 bygroove 198 and to top wall 202 by a plurality of fasteners, such asscrews, bolts or clips as previously described. Communication module 130is secured to camera chassis 124 by brackets 136 and 138 (FIG. 7), whichallow the communication module to pivot about one end 133 so that a usercan service the communication module without having to physically removeit from the camera.

When communications module 130 is in its closed position, heat sinks 240are received through chassis bottom wall openings 158. As a result,illumination module rear wall 168, camera chassis rear wall 146,communications module heat sinks 240 (only one of which is shown in FIG.15) and chassis bottom wall 140 (not shown in FIG. 15) together definecooling channel 244, which is sealed from the sensitive optics andelectronics of the camera. Each of the cooling channel walls contains aplurality of metallic fins to conduct heat away from the electricalcomponents into the cooling channel to assist in heat dissipation. Fans152 and 154, located at each end of cooling channel 244, pull air intoone end and push air out the other end of the channel to expel the heatfrom the camera. In one embodiment, a fan forced air flow ofapproximately 130 cubic feet per minute should maintain a desiredtemperature range within the camera.

Cameras 106, 108 and 110 may play different roles in a scanning tunnel.Preferably, for example, one camera is designated as the master camera.The master camera receives a trigger signal and the system tachometersignal and provides a trigger signal and focus information to othercameras in the tunnel. One camera (either the master camera or one ofthe slave cameras) is connected to the host system and is responsiblefor transmitting package data to the host system.

Data collected by each camera for a single box is combined into a singlemessage that is transmitted to the host system when the package reachesa transmit point. Bar code and package information may be transferredbetween cameras over the 100 Base-T Ethernet network. Each of cameramodules 106, 108 and 110 is capable of correlating the messages from allof the other cameras in the tunnel system and generating a combinedmessage. That is, if the master camera receives all of the camera datafrom the other cameras, it can correlate the multiple image data andtransmit the combined data to the host system. Because each of thecameras have the ability to receive data from the other cameras andcorrelate the combined data, two camera modules in the same tunnelsystem may be connected to different host systems, each with a differentdata format and transmit points. Additionally, because all of thecameras are networked, one camera could perform processing for datacollected by another camera should a camera loose the ability to processdata. Moreover, each camera contains set-up and calibration data aboutevery other camera in the tunnel system.

FIGS. 16 and 17 illustrate one embodiment of a range finder for use inthe tunnel system of FIG. 3. Range finder 102 has a housing 246 formedfrom a front wall 248, a top wall 250, a bottom wall 252, a back wall254 and two end walls 256. Referring to FIG. 18, front wall 248 definesthree circular openings 258, 260 and 262 and one rectangular opening264. Two brackets 266 and 268 are mounted to end walls 256 and allow therange finder to be mounted to the frame of the tunnel system.

Range finder 102 has two laser illumination devices 270 and 272 mountedproximate each end of housing 246 in respective openings (not shown).The laser devices are fastened to housing 246 and secured in place bycover plates 274 and 276 (FIG. 17). A respective front end 282 and 284of the laser illumination devices extend into respective front wallopenings 258 and 262. Each laser device front end 282 and 284 isenclosed by a respective diffractive optical element and covered bycovers 286 and 288 having a clear window, which are fastened to rangefinder front wall 248 over openings 258 and 262 by fasteners or othersuitable connecting devices. A range finder linear sensor board 290 isreceived in a rectangular opening (not shown) formed in housing backwall 254 and is secured in place by a cover plate 292 by screws, boltsor other suitable fasteners. A sensor head 296 extends through housingfront wall opening 260 so that the sensor optics are covered by a lenscover 298, which is fastened to housing front wall 248. A control panel300 is received in housing front wall rectangular opening 264 and issecured in place with screws, bolts or other suitable fasteners.

Referring to FIG. 19, laser illumination devices 270 and 272 and theirrespective diffractive optical lenses (not shown in FIG. 19) are used togenerate a laser pattern 302 with a spatially-unique bar arrangement(FIG. 20). Laser illumination devices 270 and 272 are placed at an angleθ with respect to an axis 308 normal to conveyor 104. Referring to FIG.21, the spatially-unique bar arrangement consists of a series of longlighted bars 314 and short lighted bars 316 that are separated by shortblank (non-lighted) spaces 318 and long blank (non-lighted) spaces 320.Narrow lighted bars are one pixel wide, narrow blank spaces are twopixels wide, wide lighted bars are three pixels wide and wide blankspaces are four pixels wide. The spatially-unique bar arrangementcontains one hundred and ninety-nine words, where a code word is definedby six elements and is approximately twenty pixels wide. The uniquepattern is defined by seventy-eight words and repeats three times tofully cover the belt width. In one embodiment of the unique pattern,there will never be three wide bars or blank spaces in a row. Thus, ifthree elements are consecutive and of similar widths, they must benarrow bars or spaces. The spatially-unique bar arrangement is alsoknown as a T-bar sequence.

It should be understood by one skilled in the art that as laser pattern302 spreads to the outer extents of the belt, the elements increase inwidth. Moreover, when a box intersects laser pattern 302, the portion ofthe pattern on the top of the box will compress in width since thedistance to the top of the box from the laser source is shorter than thedistance to the belt. However, because all of the bars and spacescompress, the unique words remain unchanged and does not effect theoperation of the range finder.

In some embodiments, the diffractive optical elements may generate aseries of light dots across the width of the belt instead of the uniquecode word pattern. However, the series of light dots are subject to thesame alignment problems that exist with prior art dimesioner designssince the line of dot must be properly aligned with the field of view ofthe linear sensor. In an effort to overcome the alignment issues, inother embodiments equally spaced light bars may be used where the heightof each bar is multiple pixels high. In the case of the equally spacedbar pattern, the alignment problem is overcome since acceptablealignment error is increased based on the height of the bars. However,both the equally spaced light dots and equally spaced light bars bothsuffer from overlap problems. That is, if the dots and bars are notsufficiently spaced apart, then one dot or bar may shift more than thespacing between adjacent dots or bars resulting in an incorrect heightmeasurement calculated for the box. If the spacing between dots or barsis narrowed to increase the resolution of the range finder, the maximumbox height for the system will be limited. If, on the other hand, thedot or bar spacing is increased to accommodate large box heights, theresolution of the dots or bars across the belt is reduced. With largespacing between the dots or bars, while the box height may be obtained,the ability to accurately detect the extents of the box is diminished.Thus, substituting the unique laser code word pattern in place ofequally spaced dots and bars overcomes both the sensor alignment andoverlap issues.

An optical axis 304 and 306 of each laser device is offset from anoptical axis 308 of linear camera sensor 296 by a predetermined distance310 by an angle θ, which allows for the linear sensor to be positionedtransverse to conveyor belt 104 instead of being parallel with the axisof travel of conveyor 104. Angle θ is used by the range finder processorto determine the height of a package using known triangulation methods.The purpose of having two laser devices 270 and 272 is to eliminate theeffect of shadowing caused by a single light source. That is, if asingle laser source 270 is used, then the portion of belt 104 adjacentto the left side of an object traveling down conveyor 104 will not beilluminated by the laser pattern since the object will block thisportion of the belt from being illuminated. Consequently, the additionof second laser device 272 allows for each laser device to be cycled onand off at a rate that causes a complete scan line to be projected ateach point along the length of the belt, thereby effectively eliminatingthe effects of shadowing.

As an object passes into illumination laser device fields of view 302,the spatially-unique bar arrangement shifts transverse to the directionof travel on conveyor 104, which is sensed by a field of view 312 oflinear sensor 296. Because the laser pattern across the belt is unique,the shifted portion of the pattern can be detected, and based on knowntriangulation methods the amount of shift can be translated into aheight for the detected object. The extent of the pattern found at theobject height indicates the left and right extents of the object. Theobject height and extent information is correlated with tachometer countinformation and transmitted over Ethernet network 114 to camera modules106, 108 and 110, and the resultant package information is used to drivecamera focus servo module 212. Range finder linear sensor board 290contains a processor (not shown) that captures images picked up bysensor 296, processes the images to determine if objects are presentwithin range finder field of view 312 and determine the object's heightand extents (left and right edges) on a line-by-line basis.

In one embodiment, linear sensor 296 is a Toshiba 1209D 2000 pixel,single tap, charged coupled device sensor and the processor is ani.MX31L processor manufactured by Freescale Semiconductor of Austin,Tex. For a belt speed of six hundred and twenty feet per minute, rangefinder 102 can perform 2,480 sample lines per second, which yields aresolution of 1/20^(th) of an inch in the direction of travel andproduces a video rate of about five megabytes per second. Laserillumination devices 270 and 272 operate at 658 nm wavelength and thelaser is collimated with a spot diameter of 2.5×7.0 mm. Each laserillumination device and DOE is offset 20 inches from the center ofconveyor 104, and laser devices 270 and 272 are directed at a 13.94degree angle θ with respect to axis 308. The range finder image plane islocated 76 inches from the plane of the conveyor. In this configuration,the system can accommodate a maximum package size of 36 inches wide and36 inches high. It should be understood that other configurations arewithin the scope of the present invention and the above configuration ismerely presented as one example configuration. For example, the maximumbox height that can be detected by range finder 102 without a uniquecode word shifting from one portion of the unique pattern to a portionwhere the pattern repeats is approximately 50 inches high. Thus, theposition of the laser devices can be placed in other configurations toaccommodate box heights up to 50 inches tall.

In operation and as previously described, range finder 102 detects theheight of objects moving along conveyor belt 104 by detecting thelongitudinal shift of a laser pattern projected across the belt when theobject intersects the laser pattern. In particular and referring toFIGS. 24 and 25, a box 103 is shown moving along conveyor 104 indirection 26. Laser 270 projects the unique laser line pattern sequenceacross the width of belt 104. As box 103 passes through the lightpattern, a portion 315 of the unique code shifts to the right since thebox is present. A portion of the unique line pattern 105 is not seen onthe belt due to shading caused by box 103. The linear range findersensor is positioned transverse to the direction of belt travel anddetects a series of light and dark areas along the width of the belt.These light and dark areas are converted to a detected illuminationintensity signal that is used by the range finder processor to detectthe edges of the bars and spaces.

Referring to FIGS. 26 and 27, the illumination intensity signal is shownplotted versus pixel number in graph 600. The range finder processorcarries out an edge detection programming routine by first selecting asliding window 602 of twenty pixels and then calculating an averageillumination intensity 604 over the twenty pixel window. If theintensity between adjacent pixels P_(i) and P_(i+1) cross averageintensity line 604, an edge between a lighted bar and a non-lightedspace is determined to be present between pixels P_(i) and P_(i+1). Thefollowing linear interpolation formula is used to calculate theapproximate position of an edge with respect to a particular pixelP_(i):

Offset=(Average Intensity_(twenty pixel window) −P _(i intensity))/(P_(i+1 intensity) −P _(i intensity))

The actual location of an edge is equal to P_(i)+Offset. Window 602 isshifted by one pixel and the average intensity calculation is repeatedanother edge is detected and the process is repeated until all edgelocations are detected across each the width of the sensor array. Itshould be understood that if the intensity increases from P_(i) toP_(i+1), then the transition is from a bar to a space, and if theintensity decreases from P_(i) to P_(i+1), then the transition is from aspace to a bar.

After all edge locations are detected across the width of the belt, therange finder processor calculates the width of a bar or space based onthe following formula:

Width_(i)=edge location_(i+1)−edge location_(i)

Once all bar and space widths have been determined, code word extractionis performed by examining six consecutive widths: three bars and threespaces. For the three bars, the widest (W) and narrowest (N) bars aredetermined. If W/N> 7/5 and W−N>2.5 then there exists at least one widebar and a least one narrow bar. Otherwise, all three bars must be narrowsince, in one embodiment, there cannot be three adjacent wide bars. Ifit is determined that one wide bar and one narrow bar exists, then ifthe middle bar width>(W+N)/2, then the third bar is also wide, otherwisethe third bar is narrow. The above code word calculations are repeatedfor all spaces between the bars. The pixel widths of each of the narrowand wide bars and spaces drive the above rations for determining whetherdetected edges define a wide or narrow bar or space. At this point, theprocessor can determine the order of bars and spaces and the location ofthe code words with respect to the width of conveyor belt 104.

In the above described embodiments, the heights of boxes placed on theconveyor should not be larger than 51 inches to ensure that a shiftedcode word does not move into the repeated portion of the unique pattern.If, on the other hand, a box having a height greater than 51 inches isplaced on the conveyor causing a code word to shift into the repeatedportion of the unique pattern, the measured height of the box would notbe accurate. However, a disambiguation step can be performed to ensurethat larger boxes are properly measured so that the cameras areaccurately focused.

As previously described, a fundamental property of the unique barpattern is that each instance of a codeword is located in at most threedisjointed locations across the width of the belt since the uniquepattern repeats approximately two and one-half times, Thus, to accountfor the possibility of a codeword shifting into the repeated portion ofthe pattern, a photo-eye or light curtain (not shown) may be placedupstream from range finder 102 to detect when a box greater than 51inches approaches the range finder. If the photo eye or light curtain(not shown) detects a box greater than 51 inches in height, the rangefinder processor adds 51 inches to the measured height of the box. Thatis, because a shift in a code word will move into the repeated portionof the pattern when a box is greater than 51 inches, the measured heightof the box would be the actual height minus 51 inches. For example, if abox having a height of 53 inches passes under range finder 102 and acode word from the first portion of the pattern shifts into the secondrepeated portion, then the measured height of the box would be based onthe amount of shift of the code word from the original location of thesecond occurrence of the code word and not the amount of the shift fromthe original first occurrence of the code word. As such, the calculatedheight of the box would be two inches instead of 53 inches. Thus, toaccount for disambiguation, the system adds 51 inches to the measuredshift resulting in the correct height of the box.

After disambiguation, the range finder processor calculates the shift incode words. When the range finder is manufactured, a memory table isstored containing the pixel location of each code word at a far field(calibrated) which, in one embodiment is calculated at approximatelyseventy-six inches. Based on the pixel location of the shifted code wordand the pixel location in the far field for the code word, the code wordshift is calculated in pixel distance using the following formula:

Code Word Shift=Pixel location_(near field)−Pixel Location_(far field)

The range finder processor calculates the shift of each code word acrossthe top of the box for each scan in pixels and converts the code wordshift from pixel distance to inches using know conversion techniques. Inone embodiment, the height h=code word shift*tan θ.

The range finder also detects the right and left extents of the box bydetecting interruptions in code words, for example when two adjacentwords are not in the correct order. That is, because the laser lightprojects from the left or right side of the belt, the last code word onthe conveyor at the base of the box and the first code word on the topedge of the box will not be properly sequenced since a number of wordswill be projected onto the side of the box. Therefore, abrupt changes inthe unique sequence will alert the range finder processor that an edgeof the box has been detected. The same will be true on the oppositeextent of the box furthest from the laser source. Because the boxcreates a shadow, there will be an abrupt change in the code wordsequence at the furthest extent of the box and the belt.

At this point, a single slice profile of box 103 is stored in the rangefinder memory similar to prior art dimensioners. The range and extentinformation is transmitted to each camera and the information is used tofocus the cameras. Range finder 102 takes multiple scans of box 103 overtime and uses the height and extent information to build a 3-D model ofthe box. The 3-D model of the object and any barcode data obtained bythe cameras in the tunnel are transmitted to the host system for furtherprocessing.

While one or more preferred embodiments of the invention have beendescribed above, it should be understood that any and all equivalentrealizations of the present invention are included within the scope andspirit thereof. The embodiments depicted are presented by way of exampleonly and are not intended as limitations upon the present invention.Thus, it should be understood by those of ordinary skill in this artthat the present invention is not limited to these embodiments sincemodifications can be made. Therefore, it is contemplated that any andall such embodiments are included in the present invention as may fallwithin the scope and spirit thereof.

1. A method for measuring a height of objects on a moving surfacecomprising: a. providing (i) a linear image sensor positioned transverseto a direction of travel of the moving surface, and (ii) at least onelight source positioned collinear to said linear image sensor andproximate to an edge of the moving surface so that said at least onelight source projects a unique patterned light sequence across a widthof the moving surface; b. detecting a transverse shift in a portion ofsaid unique patterned light sequence with respect to the direction oftravel of the moving surface as an object passes through said uniquepatterned light sequence; c. determining an amount of shift of saidportion of said unique patterned light sequence; and d. determining aheight of the object based on said portion of said unique patternedlight sequence shift.
 2. The method for measuring a height of objects ona moving surface of claim 1, said unique patterned light sequencecomprising a series of light bars separated by non-lighted spaces. 3.The method for measuring a height of objects on a moving surface ofclaim 2, said light bars and non-lighted spaces having at least twodiffering widths.
 4. The method for measuring a height of objects on amoving surface of claim 3, said light bars having at least two differingwidths and said non-lighted spaces having at least two differing widthsthat also differ from said at least two differing light bar widths. 5.The method for measuring a height of objects on a moving surface ofclaim 2, wherein said series of light bars and said non-lighted spacesdefine a plurality of words across the width of the moving surface. 6.The method for measuring a height of objects on a moving surface ofclaim 5, wherein a width of said light bars are selected fromapproximately one and three pixels and a width of said non-lightedspaces are selected from approximately two and four pixels.
 7. Themethod for measuring a height of objects on a moving surface of claim 5,wherein the step of detecting a transverse shift further comprises: a.detecting edges of said light bars; b. determining a sequence of saidlight bars and said non-lighted spaces; and c. extracting at least oneof said plurality of words based on said sequence of said light bars andsaid non-lighted spaces.
 8. The method for measuring a height of objectson a moving surface of claim 7, wherein the step of determining a heightfurther comprises comparing said amount of shift of said at least one ofsaid plurality of words to a predetermined location of said at least oneof said plurality of words when the object is not present.
 9. The methodfor measuring a height of objects on a moving surface of claim 1,wherein said unique patterned light sequence is formed by a diffractiveoptical lens.
 10. The method for measuring a height of objects on amoving surface of claim 1, wherein said unique patterned light sequenceis a T-bar sequence.
 11. The method for measuring a height of objects ona moving surface of claim 2, wherein said light bars and non-lightedspaces have a length in the direction of travel of the moveable surfaceof at least 3 pixels.
 12. The method for measuring a height of objectson a moving surface of claim 2, wherein the step of detecting saidlighted bar edges further comprises the steps of a. detectingtransitions from lighted bars to adjacent non-lighted spaces; and b.using linear interpolation to determine the approximate pixel locationof each of said transitions.
 13. A method for measuring a height ofobjects on a moving surface comprising: a. providing (i) a linear imagesensor positioned transverse to a direction of travel of the movingsurface, and (ii) a first and second light source that project a uniquesequence of lighted bars having differing widths and non-lighted spaceshaving differing widths across the width of the moving surface, whereinsaid first and second light sources are spaced apart from each other onopposite sides of the moving surface; b. detecting a shift in a portionof said unique sequence of lighted bars and non-lighted spaces as anobject passes through said unique light sequence; c. determining anamount of shift of said portion of said unique light sequence; and d.determining a height of the object based on said amount of shift of saidportion of said unique light sequence.
 14. The method for measuring aheight of objects on a moving surface of claim 13, wherein said firstand said second light sources are alternately cycled on and off.
 15. Themethod for measuring a height of objects on a moving surface of claim13, wherein said step of detecting a shift further comprises: a.detecting edges of said lighted bars; b. determining a width of saiddetected lighted bars and respective adjacent non-lighted spaces; and c.extracting at least one of a plurality of code words based on a sequenceof said lighted bars and said non-lighted spaces, wherein said code wordis defined by at least two lighted bars and two non-lighted spaces. 16.The method for measuring a height of objects on a moving surface ofclaim 13, wherein a width of said light bars are selected fromapproximately one and three pixels and a width of said non-lightedspaces are selected from approximately two and four pixels.
 17. Themethod for measuring a height of objects on a moving surface of claim13, wherein said light bars and non-lighted spaces have a length in thedirection of travel of the moveable surface of at least 3 pixels. 18.The method for measuring a height of objects on a moving surface ofclaim 15, wherein the step of detecting said lighted bar edges furthercomprises the steps of c. detecting transitions from lighted bars toadjacent non-lighted spaces; and d. using linear interpolation todetermine the approximate pixel location of each of said transitions.19. The method for measuring a height of objects on a moving surface ofclaim 18, wherein the step of determining a height further comprisescomparing said amount of shift of said at least one of said plurality ofwords to a location of at least one of said plurality of words when theobject is not present.
 20. A range finder for measuring the height ofobjects on a moving surface comprising: a. a linear image sensorpositioned transverse to a direction of travel of the moving surface; b.at least one light source positioned collinear to said linear imagesensor and proximate to an edge of the moving surface, wherein saidlight source projects a unique sequence of light bars and respectiveadjacent non-lighted spaces across a width of the moving surfacetransverse to the direction of travel; and c. a processor operativelyconnected to said linear image sensor and said at least one light sourcefor calculating a height of the object as it passes through said uniquesequence of lights bars and respective adjacent non-lighted spaces. 21.The range finder of claim 20, said light bars having at least twodiffering widths and said non-lighted spaces having at least twodiffering widths that differ from said at least two differing light barwidths.
 22. The range finder of claim 20, wherein a series of light barsand adjacent non-lighted spaces together form a plurality of uniquewords.
 23. The range finder of claim 20, further comprising a secondlight source positioned collinear to said linear image sensor and saidfirst light source proximate to an opposite edge of the moving surface.24. The range finder of claim 21, further comprising at least onediffractive optical element for forming said unique sequence of lightbars and respective adjacent non-lighted spaces.
 25. The range finder ofclaim 23, wherein said first and said second light sources alternatelyilluminate said belt at a predetermined frequency.